Chronic infection with the hepatitis B virus (HBV) is a major global health problem. HBV is the prototype member of the Hepadnaviridae family, which have a strong preference for infecting liver cells (Ganem et al, 2004).
Despite the availability since three decades of an efficacious preventive vaccine for the protection against hepatitis B, an estimated two billion people have nevertheless been infected with HBV and more than 240 million currently have chronic (long-term) hepatitis B infection, with a geographical predominance in regions outside Western Europe and North America (World Health Organization, July 2013).
Transmission of the virus between people occurs by direct blood-to-blood contact or via semen or vaginal fluid of an infected person. In endemic areas, the infection occurs characteristically by perinatal transmission from mother to child. Thus, although HBV is not transmitted casually, the virus—via similar modes of entry as human immunodeficiency virus (HIV) but being at least 50 times more infectious—can be easily transmitted by perinatal, percutaneous or sexual exposure. Frequent person-to-person contact with infected individuals accordingly poses a serious risk to groups like health workers.
Infection with HBV can develop as an acute viral hepatitis, an illness that begins with general ill-health, loss of appetite, nausea, vomiting, body aches, mild fever, and dark urine, and then progresses to development of jaundice. The illness lasts for a few weeks and then gradually improves in most affected adults. A few people may have more severe liver disease (fulminant hepatic failure), and may die as a result. The infection may be entirely asymptomatic and may go unrecognized. Chronic infection with hepatitis B virus either may be asymptomatic or may be associated with a chronic inflammation of the liver (chronic hepatitis), leading to cirrhosis over a period of many years. This type of infection dramatically increases the incidence of hepatocellular carcinoma (liver cancer), also with a latency of many years.
Treatment of chronically HBV-infected individuals with antiviral drugs such as nucleoside/nucleotide analogues (e.g. Entecavir and Tenofovir) or interferon (IFN)α efficiently decreases serum viral loads. However, antiviral therapy rarely leads to a sustained virological response and drug resistance occurs (Zoulim et al., 2012). Moreover, the great majority of HBV carriers remains untreated.
Approximately 15-40% of chronic HBV carriers will develop clinically significant liver diseases in their lifetime with a high risk of death from liver cirrhosis and associated liver failure or hepatocellular carcinoma (HCC) (Lok, 2002; and Huang et al., 2011). Yearly up to one million people die worldwide due to the acute or chronic consequences of hepatitis B (Michel et al, 2001; Grimm et al, 2013). Due to the failure of antiviral drugs to eradicate infection, and consequently the need for long-term if not lifelong antiviral therapy with its drawbacks such as toxic side-effects and high costs, there is an urgent need for novel therapeutic approaches (Grimm et al., 2013).
The present invention is meant to enable efficacious therapeutic vaccination against chronic HBV infection. Therapeutic vaccination constitutes a promising strategy to treat chronic hepatitis B (Michel et al., 2011).
Next to the humoral immune response against HBV, which is predominantly involved in the protection against HBV infection by the current prophylactic vaccines (Lok, 2002), the cellular immune response is unequivocally involved in the natural resistance against HBV infection.
Perinatal transmission of HBV from mothers to neonates and infections during the first years of life result in persistent infection in more than 90% of children. By contrast, infection during adulthood clears spontaneously in more than 90% of cases and results in lifelong protective immunity (Rehermann et al., 2005).
In acute, self-limited hepatitis B virus infection, vigorous polyclonal and multispecific CD8+ cytotoxic T cell (CTL) and CD4+ T-helper (Th) cell responses to many HBV antigens are readily demonstrable in the peripheral blood (Michel et al., 2011).
These T cell responses are crucial in HBV clearance and control. Experiments in HBV-infected chimpanzees have shown the essential role of HBV-specific CD8+ T cells as effector cells in this process (Thimme et al., 2003). In contrast to the response in patients with resolved HBV infections, in patients with chronic hepatitis B the T cell responses are usually very weak, focused on only a few epitopes and functionally impaired (Michel et al., 2011). The goal of therapeutic vaccination is to install vigorous and robust multivalent CTL and T-helper cell responses directed to many HBV antigens, thereby pursuing viral clearance, hepatitis control and cure.
Despite the fact that great progress has been made in understanding the etiology and epidemiology of the disease, there is still a need for an effective therapeutic HBV vaccine.